Conventional automatic transmissions include a torque converter that receives torque from an engine and planetary gearsets that receive torque from the torque converter. The planetary gearsets provide various gear ratios of torque and thus various drive speeds. Transmissions also typically include fluid pressure-operated, multi-plate drive or brake clutches and/or brake bands that are connected to the individual elements of the planetary gearsets in order to allow shifts between the various gear ratios. In addition, automatic transmissions may also include one-way clutches (i.e., overrunning clutches) that cooperate with the multi-plate clutches to optimize power shift control. Finally, typical transmissions include a controller for selectively applying and releasing elements to shift the gears.
The inventors have herein recognized a need to provide a transmission having a main drive assembly and an underdrive assembly that improves vehicle performance and has a modular design to reduce complexity of assembly.